The present invention relates to a novel device for measuring a transverse dimension of a thread-like structure, and in particular of a yarn running on a textile machine. Such a measuring device is, among others, of importance for detecting and eliminating yarn faults with the aid of electronic yarn clearers.
Devices for recording various variable processes with the aid of linear or two dimensional arrays of optoelectrical sensors are known. In German Pat. No. 1,216,589 there is described an arrangement for mechanical detection of characters passing with a constant speed by a sensing zone, where the information content appearing in the sensing zone is supplied to a matrix memory. The characters are sensed by a double row of photosensors, where the sensors of one row are staggered to the ones of the other row, in order to ensure uninterrupted sensing. The binary signals furnished by the sensors in any sensing cycle are processed in parallel. Any character is read in five consecutive sensing cycles in the direction of reading, and the binary signals gained in one cycle are stored in one of five storage rows. Each storage row comprises a multiplicity of storage units the number of which is greater than the number of sensors.
This manner of sensing has up to now not yet gained acceptance in the technology of measuring running yarns, threads, slivers etc. though it implies certain advantages in the textile industries.
Thus, with the conventional optoelectrical measuring devices which are used e.g. in optoelectronic yarn clearers, the continuous detection of the transverse dimension of the yarn causes serious difficulties since the measuring signals furnished by the sensor always comprise the ground signal brought about by the empty measuring area, combined with the relatively small yarn signal which represents the transverse dimension. Thus, any changes of the ground signal due to ageing of the structural parts and, in particular, to dirt or contamination of the optics also affect the yarn signal. Now it is difficult or even impossible to continuously compensate or eliminate those undesired changes during the working process and, in particular, when clearing yarn in the winding plant. Above all, unsymmetrical dirt distribution in the optics is a problem which up to now has not been dealt with, much less solved.